Compounds containing two or more hydroxyl groups find use in a broad range of industrial applications. They are key components in such materials as polyesters, urethane foams and resins, and as intermediates for the preparation of surfactants. Two compounds having potential for use in such applications are 3,4-dideoxyhexitol and 2,5-bis(hydroxymethyl)tetrahydrofuran. However, previous methods for the preparation of these compounds have been too costly to be of commercial interest.
In 1933, Zartman and Adkins, J. Am. Chem. Soc., 55, 4559-4563 (1933), reported the hydrogenolysis of sugars using copper-chromium oxide in ethanol solution at about 300 atmospheres pressure. The main product of this reaction was propylene glycol. Smaller amounts of other alcohols were formed in this reaction. Certain of the sugars gave small amounts of a tetrahydroxy compound, tentatively identified as 3,4-dideoxyhexitol (hexanetetrol-1,2,5,6).
Later, Gorin and Perlin, Can. J. Chem., 36, 661-666 (1958) obtained 3,4-dideoxyhexitol in 4.3% yield by hydrogenolysis of 1,2-0-isopropylidene-D-glucofuranose. Still later, Kuszmann and Sohar, Carbohydrate Research, 83, 63-72 (1980), disclosed a multistep process for the conversion of mannitol to 3,4-dideoxy-D-threo-hexitol and for the conversion of glucitol into 3,4-dideoxy-erythro-hexitol. None of these methods are practical as a commercial synthesis of 3,4-dideoxyhexitol.
U.S. Pat. Nos. 3,040,062 and 3,083,236 disclose the preparation of 2,5-bis(hydroxymethyl)tetrahydrofuran by the catalytic hydrogenation of 5-(hydroxymethyl)furfural, an expensive starting material.
The present invention involves the discovery that certain sugars or hexitols can be converted directly to 3,4-dideoxyhexitol in greatly improved yields when the starting materials are subjected to hydrogenolysis in the presence of a suitable catalyst. The hexitol is readily dehydrated with ring closure to give 2,5-bis(hydroxymethyl)tetrahydrofuran.